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muscle plasma membrane
cytoplasms of a muscle cell
myo, mys, and sarco refer to what?
bundle of muscle fibers
- long, cylindrical cell
- multiple nuclei underneath sarcoloma
- (muscle fibers)
- contractile elements
- most of muscle volume
- smallest contractile unit of muscle
- 2 types- thick and thin
- thick filaments
- thin filaments
- extend the entire length of an A band
- extend across the I band and partway into the A band
- actin, tropomyosin and troponin
- or Z line
- coin shaped sheet of proteins (connnectins) that anchors the thin filaments and connects myofibrils to one another
thin filaments do not what?
overlap thick filaments in the lighter H zone
tropomysosin and troponin
regulatory subunits bound to actin
sliding filament model of contraction?
- in relax state, thin and thick filaments overlap only slightly
- upon stimulation, myosin heads bind to actin (cross bridge formation) and sliding begins
- think filaments slide past thick filaments
- overlap of actin and myosin filaments increases
skeletal muscle contraction
- 1. be stimulated by nerve ending
- 2.produce an electrical current, or action potential, along the sarcolemma
- 3.have a ruse in intracellular Ca levels
skeletal muscles are stimulated by what?
motor neurons of the somatic nervous system
each muscle is served by?
one nerve containing numerous neurons
each neuron controls what?
a number of muscle fibers (motor unit)
what is acetyl choline?
nerve stimulus of skeletal muscle (phase 1)
- Acetyl Choline is released from presynaptic neuron
- ACh binds its receptors at the postsynaptic motor end plate
- binding opens chemically gated channel
- Na+ diffused through channel and the interior of sarcolemma becomes less negative (depolarization)
- depolarization leads to and action potential that spreads in all directions across the sarcolemma
when Na+ diffused through channel and the interior of sarcolemma becomes less negative
lose K and gain Na
- immediately after the depolarization wave passes, Na+ channels are closed and K+ channels open
- K+ diffused from the cell, restoring the electrical polarity in the sarcolemma
sarcoplasmic recticulum (SR)
- regulates intracellular calcium levels
- (like the smooth endoplasmic reticulum)
- penetrate into the cell's interior at each A abnd band junction
- associate with the terminal ciscternae to form triads
- they conduct action potentials to the deepest regions of the muscle
- and signal the release of Ca
- AP travels across the entire sarcolemma
- AP travels along T tubules
- SR releases Ca; Ca binds to troponin; myosin-binding sites (activate sites) on actin exposed
- myosin heads bind to actin;contracting begins
myosin head pivots and oulls actin filament toward M line
axon terminal does what?
attaches to neuron
a motor neuron and all the muscle fibers it supplies
contraction of a single motor units does what?
causes a weak contraction in the entire muscle
muscle that control fine units (fingers and eyes)
have small motor units
large weight-bearing muscles(thing, hips)
have large motor units
graded muscle responses
- variations in the degree of muscle contraction
- it varies in the # of motor units involved and changing of frequency of stimulation
the responses of a a muscle (single motor unit) to a single, brief threshold stimulus
three phases of a muscle twith?
- latent period
- period of contraction
- period of relaxation
excitation contraction coupling is taking place( getting ready to contract, very short)
period of contraction
cross bridges actively form and the muscle shortens
period of relaxation
Ca is reabsorbed into the SR and muscle tension goes to zero
a single stimulus results in a single contractile reponse
frequently delivered stimuli (muscle does not have time to relax) increases contractile force (harder twitch)
- continuous, repeated stimuli results in a maximal sustained contraction
- the muscle locks up
the force of contraction is precisely controlled by what?
multiple motor unit summation
as more neurons are activated, more motor units are stimulated to contract
refers to the force generated by the formation of myosin across bridges
tension generated by the cross bridge exceeds forces opposing shortening
increasing muscle tension (muscle does not shorten during contraction)
isotonic (concentric) contraction
decreasing muscle lengh (muscle shortens during contraction)
the muscle contracts as it lengthens
- creatine phospahte 1
- anaerobic glycolysis 2
- aerobic respiration 3
the muscle is in a state of physiological inability to contract
what causes muscle fatigue?
- ATP production fails to keep pace with ATP use
- Myosin crossbridges cannot slide and get "stuck" causing contractures
- the inability to mantain na and K gradients
- lactic acid accumulates and causes pain
what must happen so muscle can return to a resting state?
- oxygen reserves must be replenished
- ATP and CP reserves must be resynthesized
- lactic acid must be converted to pyruvic acid
- glycogen must be replaced
the extra amount of O2 needed for the muscle to return to a resting state
- quick but inefficient supply of ATP
- requires alot of glucose
- slow but alot of ATP
- response is limited by krebs cycle and ETC
fast muscle fibers
- need alot of glucose
- rapid power contractions
- sustained contraction
wavelike series of contractions that move things in smooth muscle like food
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